As shown in FIG. 1, a typical fiber grating-based strain sensing system 10 for sensing a measurand field according to the prior art comprises an optical source 20 for providing broadband light 25 to an array 30 of serially coupled sensor elements 40. Each sensor element 40 returns an optical signal 50 having a narrow-band wavelength component, the wavelength depending by a known functional relation on the measurand field being sensed. The measurand field is a particular environmental condition or physical phenomenon under consideration. In other words, perturbation of that condition or phenomenon at element 40 results in a change of the wavelength of optical signal 50. The array 30 combines the individual signals, such as by wavelength-division or time-division multiplexing, to produce a composite return signal 60 having a plurality of components, each uniquely corresponding to a signal 50 from an individual sensor element 40.
The return optical signal 60 is decoded by decoding device 65 to provide signals 70, each of which corresponds to a signal 50 from a selected element 40 and is indicative of the measurand field value at that selected element 40. Signals 70 are processed by signal processing circuits (not shown) to identify the wavelength shift and produce output signals indicative of the measurand field values at elements 40. This processing typically utilizes a bulk-optical spectrometer, monochromator, or dispersive element coupled with an image array, such as a CCD detector array.
These systems according to prior art are unattractive due to the nature of a bulk-optical apparatus, its size, and its lack of ruggedness. Furthermore, conventional optical sensing systems provide low resolution and accuracy since the resolution of even the best spectrometer is about 0.1 nanometer (nm) or less, which is typically on the same order of magnitude as the optical bandwidth of the sensor elements.